[Wien] SCF with force convergence

[Stefaan Cottenier]

> Can you please eleborate
> 
> "there are no atoms with a free parameter in their coordinates"
> 
> I dont understand what the free parameters are? 

They are the coordinates indicated by x, y and z in the list of special 
positions as given in crystallographic tables. Example: position 12e in 
spacegroup Im-3m ( 
http://www.cryst.ehu.es/cgi-bin/cryst/programs/nph-wp-list?gnum=229 ). 
In contrast to position 12d where all 6 atoms are completely determined, 
there is one degree of freedom in 12e given by 'x'. The presence of such 
a free parameter corresponds with a force in wien2k.

> For instance i am 
> working with Wurtzite GaN doped system wherein i am not able to get 
> convergence of 5 mRy/a.u. We have used the experimental lattice constant 
> and formed the unit cell from which a supercell was generated.

In order to do relaxations around impurities, it is better to work with 
the calculated lattice constants of the pure compound. But that's not 
the origin of your problem. Are your k-mesh and basis set large enough 
(= did you check the stability of forces which respect to them)? Is the 
choice of linearization energies OK? etc...

Stefaan